1. Field of the Invention
The present invention relates to a pulse motor control device, a control method, a control program, and imaging apparatus.
2. Description of Related Art
There is provided imaging apparatus that pans and tilts a video camera for capturing, by an imaging element, a subject image introduced through a photographic optical system.
Such imaging apparatus is used to form a surveillance camera system for monitoring an outdoor or indoor area, or to form a television conference system for shooting participants of a conference, for example.
In many cases, in such imaging apparatus, a pulse motor (stepping motor) is used as a drive source for swiveling a video camera around a virtual axis extending along the vertical direction (swiveling the video camera in the pan direction) and a drive source for swiveling the video camera around a virtual axis extending along a direction perpendicular to the vertical direction (swiveling the video camera in the tilt direction).
The pulse motor allows easy position control through only counting of the number of drive pulses, but is disadvantageous in smooth low-speed rotation.
Meanwhile, enhancement in the image quality and increase in the number of pixels for video cameras are being promoted in recent years. Therefore, unless the rotation of the pulse motor is smooth in swiveling of the video camera at low speed, noticeable unnatural blurring will occur in captured video.
To address this problem, a scheme to prevent blurring in video captured by a video camera is often employed. In this scheme, segmented driving of the pulse motor is carried out based on micro-step driving to thereby allow smooth low-speed rotation by the pulse motor.
However, in the case of driving a pulse motor based on micro-step driving, more drive pulses whose number is larger by a factor of the multiple number corresponding to the number of segmentation are needed to rotate the pulse motor by the same angle as that in a normal pulse drive system.
Thus, compared with the normal pulse drive system, the micro-step driving involves increase in the number of drive pulses generated per unit time, and hence a heavier burden on the unit that generates the drive pulse.
To address this problem, a technique has been proposed. In this technique, in driving of a pulse motor based on micro-step driving, plural clock pulses are generated per one time of interrupt processing of a microcomputer, and the pulse motor is driven by micro-step driving based on the clock pulse (refer to Japanese Patent Laid-open No. Hei 11-41989).
Furthermore, another technique has also been proposed. In this technique, in driving of a pulse motor based on micro-step driving, the micro-step value of the micro-step excitation system is changed to e.g. ½, ¼, ⅛, or 1/16 depending on the rotational speed (refer to Japanese Patent Laid-open No. 2003-304698).